Portable fire extinguishers can be a useful first defence against fires –
particularly in stopping small fires taking hold. Dr Tim Nichols explains how to ensure quality provision and maintenance of these extinguishers and outlines the different types and their use on different classes of fire.
Portable fire extinguishers fulfil an important role in front line fire defence. Standards and approvals have improved substantially over the last few years, as has the range and quality of products available. This article summarises some of the products, standards and applications that are applicable to portable fire extinguishers.
Much focus has been given in recent years to the quality of provision and maintenance of portable fire extinguishers. The Fire Extinguishing Trades Association (FETA) is the association of service providers and manufacturers. It ensures quality of membership, standards and provides details of recommended training suppliers. A standard FETA examination covers the theory of fire, the types and location of portable extinguishers as well as the extinguishing agents themselves, and also the responsibilities of the employer/employee under the Health & Safety at Work Act.
British Approval for Fire Equipment (BAFE), operates third party certification schemes that apply to the operating company, as well as to registered technicians. Firms are subject to a quality scheme which includes the manufacture, contract maintenance and refurbishment of portable fire extinguishers. The registered technician scheme allows for an independent overview of technicians, a huge benefit which supplements the quality schemes applied to organisations. The British Fire Consortium (BFC), which represents a large number of smaller quality companies, and FETA, both promote and support BAFE training.
These trade bodies, together with the Fire Protection Association (FPA) and several independent organisations offer fire training that involves the practical use of portable extinguishers for staff in many different types of organisation.
Classes of fire
There has been some confusion in the past about the definition of fire classes, not least of which has been between the US fire class definitions and the UK ones. The table opposite shows the labelling of both sets of fire class definitions.
The common US/UK definitions are for Class A, B and D fires. In brief, Class A fires are carboniferous fires such as wood, paper, so most offices and accommodation would be classed principally as A-type fires. It is interesting to note a recent extension to the Class A definition to include plastic fires, to which particular attention has been drawn for tests on extinguishing agents in the new draft BS ISO14520 for fixed gas extinguishing systems. Class B fires are hydrocarbon solid or liquid fuel fires, e.g. petrol, paraffin wax, etc; and alcohol fires. Class D fires are those involving metals, such as magnesium and potassium, which react with water and other types of extinguishing media such as nitrogen and carbon dioxide. The differences between US and UK class definitions occur for electrical, gas and fat fires. The UK Class C is for gas fires, and the US Class C is for electrical fires. The UK no longer recognises electricity as a fire in itself, only as a cause of fire, whereas the US base their Class C on electrical fires. (The term Class E used to be applied to electrical fires in the UK.) Fat and cooking oil class of fires are defined under Class K in the US, and Class F in the UK.
Due to the large number of fire classes, no single portable extinguisher can extinguish all types of fires. Although we have discussed that electrical fires are not classed as a fire type, awareness needs to be made of the dangers of using a conducting medium on fires that involve electricity. Each portable extinguisher carries a pictogram and letter of the class of fire as shown in the table, and the most popular extinguishers include water, foam, dry powder and carbon dioxide. Water can have additives, for example wetting agents and potassium salt. A wetting agent reduces the surface tension and aids the fire fighting in Class A fires, while a potassium salt based agent is used for Class F fires and turns the surface of the fire into soap, which then forms a seal and effectively smothers the fire. The latter additive has been long used in fixed, pre-engineered kitchen hood systems.
Foam is an effective extinguishing agent which works by cooling the fire and sealing the fuel. Most commonly used for Class B fires, the foam is created by adding a concentrate to water. The majority of foams used are environmentally friendly but some of the more effective agents have been under environmental scrutiny. Recent examples are the disposal of AFFF pre-mix foams (which can contain additives such as anti-freeze), and perfluorooctane sulphonate (which has been found to be persistent, bio-accumul-ative and toxic). Further information can be obtained from FETA and the British Fire Protection Systems Association (BFPSA) which has a dedicated working group on these topics.
Carbon dioxide is most commonly applied on electrical fires and is effective on other fuels. It works by excluding the oxygen from the fire but despite the frosting on discharge, actually has very little cooling ability.
Standard dry powder has very fast knock properties that make it an ideal first hit agent and can be used for every type of fire, with the exception of Class D fires. In the case of Class D fires, a special dry powder specific to this type of fire is used. No other ‘local’ application method exists, but fires can be extinguished by inerting the entire volume with a non-reactive, inert gas, such as argon.
Halon 1211 BCF extinguishers have been withdrawn from service except for critical use applications. There are halocarbon replacements, the most common using FE-36 or NAFS PIV.
Each extinguisher has a rating for its fire fighting effectiveness, and a greater rating can be achieved using additives, or enhanced spray. There is much technology in the design of the nozzle itself, from the horn of a CO2 nozzle to aid the expansion of liquid into gas, to the lance of a Class F extinguisher that allows a gentle dispersion of the agent to prevent splashes from hot fires.
Some extinguishers are not covered in the British Standards detailed above – an example is portable water mist extinguishers. Portable high-pressure water mist systems tend to use a pump mounted on a trolley unit, with a lance to a nozzle. Water mist is very effective on Class B and Class F fires: these are ‘hot’ fires that draw water mist droplets into the fire. The water mist provides a large amount of cooling by turning to steam, and adds an effective smothering to the flame front.
Larger extinguisher units are available as ‘trolley’ units. They are used where more fire fighting capability is required but can be for other uses, such as a twin agent system, e.g. foam and dry powder. The dry powder knocks down the fire and the foam forms an effective seal to prevent re-ignition.
The importance of proper location, type and quantity of portable extinguishers, and training in their use and maintenance, has been recognised by government, fire brigades and the trade associations. For further reading there is a Joint Protocol published by FETA that is an initiative by the Local Government Association (LGA), the Chief Fire Officers Association (CFOA) and FETA. This covers implications of legislative change, and looks at the success in Europe of the use of portable fire extinguishes.
Portable fire extinguishers provide the best first line of defence where people are available to tackle the fire. They have saved much loss to buildings, call-outs to brigades and danger to life. The continued focus on their quality and development – as well as training in their proper use – are to be applauded.
